1. Hintzen, P., Scott, J.S.: Astrophys. J. 239 (1980) 765.
2. Int. Astron. Union Symp.;S.M. Alladin,1975
3. Allen, D.A.: Astrophys. J. 207 (1976) 367.
4. Arakelyan, M.A., Dibai, E.A., Esipov, V.F.: Astrofizika 6 (1970) 39 <14>; 8 (1972) 33 <17>; 8 (1972) 177 <106>; 8 (1972) 329 <197>; 9 (1973) 319 <180>; 9 (1973) 325 <183>.
5. Arakelyan, M.A., Dibai, E.A., Esipov, V.F., Markarian, B.E.: Astrofizika 6 (1970) 357 <189>; 7 (1971) 177 <102>.